PROJECT SUMMARY Impact: This proposal addresses the pressing need for effective treatments for cryptosporidiosis in infants. The therapeutic target is human protein kinase C (PKC?), which we recently discovered as a host susceptibility gene for cryptosporidiosis. Successful completion of this work will broadly advance the field of host-targeted therapy by taking a hit from a forward-genetic screen through mechanistic validation during disease. Significance: Cryptosporidiosis is one of the top 5 causes of diarrhea in children in low- and middle-income countries. There is no vaccine and the drugs are extremely limited with none approved for infants. Thus, there is an urgent need for effective therapies, particularly for children. This proposal sets a precedent for developing host targets for microorganisms, an area of high significance in the face of emerging antimicrobial resistance. Innovation: A genome-wide scan for infectious disease susceptibility in infants from low-resource countries had never been done until it was pioneered by our investigator team. The proposal integrates human genetics and parasite cell biology to develop the discovery of PKC? into a target for host directed therapy. Our previous work identified novel host factors that could be blocked to prevent cell-killing by Entamoeba parasites. We propose to expand this innovative approach to Cryptosporidium. This strategy is fundamentally different from traditional parasite-targeted drugs and is based on preliminary data that PKC? is a novel host susceptibility factor for cryptosporidiosis. Approach: We have discovered that human PKC? is a key component of susceptibility to cryptosporidiosis in infants using a genome wide scan for disease-associated loci. We hypothesize that PKC? is required for intracellular infection by Cryptosporidium and could be targeted to cure cryptosporidiosis. We will define the role of PKC? in a multi-disciplinary study that integrates an analysis of PKC? during natural infection in infants (Aim 1), targeted sequencing of the PKC? locus to identify the causal SNPs and mechanism of action (Aim 2), and an analysis of host PKC? during in vitro and in vivo infection studies in combination with testing of FDA- approved PKC? antagonists (Aim 3). Successful completion of this R01 will result in an Investigational New Drug Application for a host-targeted PKC drug for cryptosporidiosis. Environment: The Investigators bring strong and complementary skills to accomplish this work. Dr. Marie (PI) is an expert in host and parasite cell and molecular biology. Dr. Duggal leads an internationally regarded program in human genetic susceptibility to infection and Dr. Haque brings extensive experience in field studies in children in Bangladesh. Importantly this team is highly collaborative as evidenced by their past discoveries and co- publications. The team brings together three internationally recognized global health centers: The University of Virginia (Dr. Marie), the ICDDR,B (Dr. Haque), and John Hopkins University (Dr. Duggal). This collaboration will occur in an exciting and rigorous interdisciplinary environment.